Conventionally, a spark plug is employed for an internal combustion engine. The spark plug includes, for example, a center electrode, and a ground electrode. The center electrode and the ground electrode form a gap to generate spark. When the ground electrode absorbs heat, an action to extinguish a flame (also referred to as a flame quenching) occurs. To reduce this, a technique that tapers off a front end portion of the ground electrode has been proposed.
Related documents of such spark plug include, for example, Japanese patent application laid-open number 05-159856, Japanese patent application laid-open number 05-159857, and Japanese patent application laid-open number 2001-351761.